I looked up a video of ippondori.
When I was watching http://www.youtube.com/watch?v=jWWrCzu-AjA in the beginning it looked like it would be ikkyo, but the finish is different. Still, to me it seems ippondori and ikkyo are related.

I remember reading that O'Sensei considered ikkyo essential for aikido. Just about every lesson we train ikkyo in some form. Another thing we train just about every lesson is tenkan undo.